Evaporator and heat exchanger with external loop, as well as heat pump system and air conditioning system comprising said evaporator or heat exchanger

ABSTRACT

An evaporator including an evaporating chamber equipped with a drainage. The drainage drains accumulated liquid from the evaporator&#39;s lower parts and includes an external expansion driven injector and/or an external pump. The evaporator can be used e.g. in a heat exchanger, e.g. in a heat pump system or air condition system, and the vacuum driven injector can be integrated with an expansion device of the heat exchanger. A condenser can be used together with the evaporator in a heat exchanger of the plate type realizing an integrated superheater/supercooler. This is accomplished by the definition and use of delimited interacting zones through which the cooling medium circulates under heat exchange with itself.

FIELD OF THE INVENTION

The present invention relates generally to an evaporator and morespecifically to an evaporator equipped with drainage means for improvingits efficiency and decrease the wear of a co-operating compressor. Theinvention also relates to a condenser to be used together with saidevaporator in a heat exchanger of the plate type.

STATE OF THE ART

Evaporators and condensers are devices e.g. used for heat exchangers,such as e.g. slender tube heat exchangers, plate type heat exchangers,spiral heat exchangers etc. In a heat exchanger according to the platetype the media circulate inside alternating plates, typically made ofmetal and brazed together with sealed inlets and outlets forming closedduct systems within a package of interacting, interconnected, plates inwhich the media circulate under heat exchange. The published patentapplication WO 00/03189, A1, describes such a plate type heat exchangerin more detail.

FIG. 1 illustrates the working principle of a conventional heatexchanger with a compressor driven evaporation process. Such a heatexchanger includes an evaporation chamber 110 in which the coolingmedium absorbs heat, Q, and there-after evaporates whereupon it isdirected to a compressor 120 and then further directed to a condenserchamber 130 where said medium emits heat, Q, and condenses. The mediumis then fed back to the evaporation chamber 110 through an expansionvalve 140. A problem for the conventional heat exchanger illustrated inFIG. 1 relates to the fact that accumulated liquid in the evaporationchamber, indicated by liquid level 150 in FIG. 1, will decrease theefficiency of the heat exchanger, for reasons known to a person skilledin the art. A further problem is that said accumulated liquid alsoincreases the amount of liquid leaving the chamber 110 with detrimentaleffects for the compressor 120, as known to a person skilled in the art.

One way to increase the efficiency of the heat exchanger illustrated inFIG. 1 is to provide additional heating of the medium in zone 170 andadditional cooling of the medium in zone 160 in FIG. 1, by means of a socalled superheater/supercooler, as known to a person skilled in the art.The superheater/supercooler function will also decrease the wear ofcompressor 120 in FIG. 1, since compressor 120 will receive a decreasedamount of liquid. One problem in conventional heat exchangers is thatthese superheaters/supercoolers are realised as external units makingthe heat exchangers bulky and not always cost effective. A particularproblem relating to heat exchangers of the plate type is thataccumulated liquid medium in the lower parts of the evaporator willcause non uniform streaming with a decreased efficiency as a result.

The present invention solves or reduces the above problems.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the problems mentionedabove.

One object of the present invention is thus to provide a more efficientevaporator.

Another object of the present invention is to decrease the wear of acompressor connected to, and co-operating with, an evaporator.

Still another object of the present invention is to improve theefficiency of heat exchangers in general and heat exchangers of theplate type in particular.

Still a further object of the present invention is to provide a heatexchanger of the plate type with an integrated supercooler/superheater.

The present invention provides an evaporator equipped with drainagemeans that drain accumulated liquid from the evaporator's lower parts.The drainage means include an injector and/or a pump.

The present invention also provides a superheater/supercooler in a heatexchanger of the plate type by providing interacting delimited zones inthe heat exchanger's evaporator and condenser.

The invention is defined by the accompanying claims 1 and 6, whereasadvantageous embodiments are defined by the dependent claims 2-5 and7-14.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail below, with reference to theaccompanying drawings, of which:

FIG. 1 illustrates the working principle of a conventional heatexchanger;

FIG. 2 illustrates different embodiments of an evaporator used in a heatexchanger according to the present invention;

FIG. 3 illustrates an example of how a first plate side, i.e. an A′front side, of a plate type heat exchanger according to the presentinvention could be designed;

FIG. 4 illustrates an example of how a second plate side, i.e. a B′ rearside, of a plate type heat exchanger according to the present inventioncould be designed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A problem regarding the efficiency of an evaporator is that ideally noliquid medium should leave the evaporator, i.e. the liquid content ofthe evaporated medium should be zero, which is hard to obtain inpractise. One object of the present invention is thus to provide a moreefficient evaporator by minimising the liquid content of the evaporatedmedium leaving the evaporator.

Another problem is that a higher liquid content of the evaporated mediumwill increase the wear of the co-operating compressor connected to saidevaporator. Another object of the present invention is thus to decreasethe wear of the compressor connected to the evaporator by minimising theliquid content of the evaporated medium leaving the evaporator.

A particular problem relating to heat exchangers of the plate type isthat accumulated liquid medium in the lower parts of the evaporator willcause non-uniform streaming with a decreased efficiency as a result. Oneobject with the present invention is thus to improve the efficiency of aheat exchanger of the plate type by minimising the amount of accumulatedliquid medium in the evaporator.

Another problem regarding heat exchangers is that thesuperheater/supercooler is an external unit, making the heat exchangersbulky and not very cost efficient. Still a further object of the presentinvention is thus to provide a heat exchanger of the plate type with anintegrated supercooler/superheater.

With reference to FIG. 2, the working principle for an evaporatoraccording to the present invention will now be described. A medium, e.g.a coolant medium such as freon, circulates from an evaporation chamber110′ to a compressor 120′ and further to a condenser 130′ and finallyback into the evaporation chamber 110′ via an expansion valve 140′, inFIG. 2. According to the invention, the evaporation chamber 110′ isequipped with drainage means 160′ in its lower parts allowingaccumulated medium in a liquid state to be piloted in an externalfeedback loop. This will decrease the liquid level 150′ in theevaporation chamber and therefore increase the efficiency of theevaporator as well as decreasing the amount of liquid arriving atcompressor 120′, and as a consequence decrease the wear of thecompressor 120′, as understood by a person skilled in the art. Thedrainage means consist of a connection e.g. by a hose, pipe or tubebetween an additional outlet 410′ in the lower parts of the evaporationchamber 110′ and an additional inlet 170′ in an expansion means, such asan expansion valve 140′, in a preferred embodiment. The expansion meansmay also be a capillary tube or the like. The expansion valve 140′ isequipped with an additional inlet 170′ for the feedback drainage in thepreferred embodiment. The additional inlet 170′ in the expansion valve140′ experience a negative pressure producing an injector effect causedby the medium streaming through the expansion valve 140′ from condenser130′ to evaporator 110′ at a relatively high velocity. This injectoreffect can be exploited to transport the liquid medium from outlet 410′back into expansion valve 140′.

In an alternative embodiment, the drainage means does not lead back intothe expansion valve 140′ but into the connection between expansion valve140′ and evaporation chamber 110′, as indicated by arrow 180′ in FIG. 2.

In another embodiment, said external loop leads back directly into saidevaporation chamber 110′, illustrated by arrow 190′ in FIG. 2.

In yet a further embodiment, said drainage means 160′ comprise a pump.

Injector effects as described above may also be exploited in thesealternative embodiments. This means that an expansion driven injectorwill be used to transport the medium through the drainage meansaccording to the invention.

The evaporator, condenser and heat exchanger according to the presentinvention shall now be described in more detail for the specific casethat the evaporator and condenser are realised in form of a heatexchanger of the plate type. Plate type heat exchangers are generallyknown devices for heat exchange between different media and are used ina multitude of contexts and the present invention is not limited to anyspecial application. However, the invention is most easily applied toplate type heat exchangers of the wholly brazed type. This means thatthe heat exchanger consists of plates having a groove pattern and inletand outlet connections for the media. The plates are placed in a packageand are brazed together into a fixed unit. Separate ducts are thusformed for the media, typically circulating in opposite directionsbetween alternate pairs of plates. The inlets and outlets extend throughall plates and are thus common for the respective medium flowing in theducts. This technique is commonly known and will not be described indetail here.

For illustrative purposes only, the invention will here be described forthe particular case with a heat exchanger in which heat exchange takesplace between three media, I, II and III but the invention is applicablefor heat exchange between an arbitrary number of media. The media usedcould for instance be: I=freon, II=brine and III=water, but otheralternatives exist as known to a person skilled in the art.

Referring now to FIG. 3, a front side A′ of a plate 300 of a heatexchanger of the plate type according to the present invention isdepicted. The plate in FIG. 3 is illustrated in its correct operationalstanding position, i.e. the force of gravity is working downwards inFIG. 3. The A′ side is equipped with an inlet 305 and outlet 310 for theII medium together with an inlet 315 and outlet 320 for medium I. Abarrier D separates the media from each other so that medium II willcirculate to the left hand side of barrier D and medium I to the righthand side of barrier D in FIG. 3, i.e. in the condenser chamber 380.According to the invention, a further barrier E is provided which formsa delimited zone A″ together with a channel C″, between said zone A″ andthe condenser chamber 380 in which medium I circulates. The barriers areobtained by a suitable, interactive, groove and recess pattern betweenthe plates as known, e.g. from the document WO00/03189 and will not bedescribed in detail here.

Referring now to FIG. 4, the rear side, B′, of the plate 300 in FIG. 3is illustrated in its correct operational standing position. The B′ sidehave inlets 405 and 420 together with outlets 415 and 425 and a barrierF which separates the media from each other so that medium I willcirculate to the left, in the evaporation chamber 450, and medium II tothe right, of barrier F in FIG. 4. In addition, the invention providesan outlet 410 in the lower parts of evaporation chamber 450, connectedto the external drainage means 430, according to the present invention.The drainage means 430 have the identical function as the drainage means160′ described above with reference to FIG. 2, and can be realised inthe same way. Thus, the drainage means 430 consist of a connection e.g.by a hose, pipe or tube between outlet 410 and expansion valve 440,illustrated by arrow 460 in FIG. 4, or, alternatively, between theoutlet 410 and somewhere between expansion valve 440 and inlet 405,illustrated by arrow 470 in FIG. 4, or, alternatively, between outlet410 and an additional inlet 490, illustrated by arrow 480 in FIG. 4. Thedrainage means can exploit the injector effect described above, i.e.comprise an expansion driven injector, and may possibly also comprise apump, as explained above with reference to FIG. 2. The drainageaccording to the present invention thus automatically drains liquid fromthe evaporation chamber 450. During operation, this drainage thuscontinuously drains a relatively small amount of liquid from theevaporation chamber and then injects it back into the chamber. When theheat exchanger is turned off, or stops for some reason, liquid willaccumulate in the evaporation chamber 450 as a result. However, thedrainage according to the present invention efficiently drains theevaporation chamber 450 as soon as the heat exchanger is turned on.Thus, immediately after starting the heat exchanger, there will be arelatively large amount of liquid draining through the drainage,however, the amount of draining liquid will decrease rather fast. Thisdrainage increases the efficiency of the evaporator and the heatexchanger and decreases the wear of the compressor, as a person skilledin the art realises.

Now, with reference to FIGS. 3 and 4, the working principle for the heatexchanger according to the present invention will be described. Forpurely illustrative purposes, a heat exchanger applied for a heat pumpapplication will be described. Medium II, e.g. brine, enters at inlet305 in FIG. 3 at a relatively higher temperature, e.g. corresponding tothe ground temperature, e.g. at 12° C., and is piloted downwards in aduct chamber 385 under heat exchange with medium I, and thereafterleaves through outlet 310 at a lower temperature, e.g. 7°, to be pilotedback to the ground in a closed loop.

Inlet 315 is fed with medium I, e.g. freon, by compressor so that mediumI enters into condenser chamber 380 through inlet 315 under highpressure and high temperature, e.g. 80° C. Medium I is piloted towardsthe inlet 370 of the channel C″ under heat exchange with medium III andfurther up through the channel C″ and piloted through the delimited zoneA″ under heat exchange with itself. Thus, the zone A″ according to thepresent invention provides a double effect in that it works as asuperheater during the evaporation stage of medium I and as asupercooler during the condensing stage of medium I. Thus, medium I isfurther condensed in the delimited zone A″. This increases theefficiency of the heat exchanger and reduces the wear of the compressor,as a person skilled in the art will understand.

The medium I leaves outlet 320 at a lower temperature, e.g. 32° C., andis thereafter fed to expansion valve 440. After passing the expansionvalve 440, medium I enters through inlet 405 at a considerable lowerpressure and temperature, e.g. 2° C. The medium I starts to evaporate ata lower pressure and evaporates further when heated in evaporationchamber 450. Medium I is then piloted towards the delimited zone B″under heat exchange with medium II, to exit through outlet 415. Whenarriving at the delimited zone B″, the temperature of medium I in thisillustrative example will be around 7° C. Medium I has a heat exchangewith itself in the delimited zone B″, as described above, and is thus inthis stage, i.e. the evaporation stage, subject for above describedsuperheater function. The superheater ensures that all liquid evaporatesbefore arriving to the compressor, which will further increase theefficiency of the heat exchanger and reduce the wear of the compressor,as a person skilled in the art realises.

Furthermore, accumulated medium I in form of liquid will be fed back bythe drainage means 430 according to the present invention, as describedabove. Medium I will thereafter be directed from outlet 415, at a highertemperature, e.g. 10° C., to the compressor in a closed loop.

Thus, medium I circulates in a closed loop from evaporation chamber 450to the compressor and further to the condenser chamber 380 andthereafter back to the evaporation chamber 450 through expansion valve440. Medium I can also circulate in the feedback loop formed by thedrainage outlet 410 and the drainage means 430 according to the presentinvention, described above.

Medium III, e.g. water, enters through inlet 420 at a relatively lowertemperature, e.g. 38° C., and leaves outlet 425 at a relatively highertemperature, e.g. 44° C., since medium III has heat exchange with mediumI in the heat exchanger. Medium III enters into a duct chamber 485through an inlet 420 at a relatively low temperature, e.g. 38° C., andis piloted through said duct chamber 485 under heat exchange with saidmedium I. Said medium III then leaves said duct chamber 485 through anoutlet 425 at a relatively higher temperature, e.g. 44° C. Thus, as anet effect, medium II has given a certain amount of heat to medium III.

Although the present invention has been described in the case for anevaporator and condenser in a heat exchanger of the plate type used fora heat pump application, it shall be understood that the invention isapplicable in a wide variety of heating and/or cooling applications. Forinstance, a person skilled in the art realises that above describedprocess can realise an air condition application, the heat exchangerneed not be of a plate type etc. Furthermore, the evaporator accordingto the invention can be used not only in heat exchangers but isapplicable in any evaporating process. FIGS. 3 and 4 are not to scaleand illustrate merely the working principle of the invention by way ofexample. Therefore, a person skilled in the art can realise theinvention in many different ways without departing from the scope of thepresent invention as defined by the following claims.

1. An evaporator of plate type having at least one inlet and at leastone outlet allowing a medium to enter into and exit from saidevaporator, said evaporator comprising: a plurality of interconnectedevaporation chambers disposed in parallel, having at least one commoninlet and at least one common outlet allowing a medium to enter into andexit from said chambers; an external loop configured to drain saidmedium from lower parts of said evaporation chambers and introduce saidmedium back into the evaporation chambers.
 2. An evaporator according toclaim 1, wherein said inlet is connected to an expansion means byconnection means, said expansion means including an additional inlet,and wherein said external loop is configured to introduce said mediumback into the evaporation chambers through the additional inlet of saidexpansion means.
 3. An evaporator according to claim 1, wherein saidinlet includes an additional inlet, and wherein said external loop isconfigured to introduce said medium back into the evaporation chambersthrough said additional inlet by an expansion driven injector.
 4. Anevaporator according to claim 1, wherein said external loop comprises apump.
 5. A heat exchanger, comprising an evaporator according claim 1.6. A heat exchanger of plate type comprising: interacting alternatingplates having a groove pattern forming at least first and secondseparate duct loop systems allowing a first medium to circulate in thefirst of said duct systems under heat exchange with a second mediumcirculating in the second of said duct systems, wherein said first ductloop system comprises a part forming a plurality of interconnectedevaporation chambers having at least one common inlet and at least onecommon outlet allowing said first medium to enter into, and exit from,said chambers, wherein said evaporation chambers include an additionaloutlet connected to a drainage means for said first medium from saidevaporation chambers' lower parts in an external loop and to introducesaid first medium back into said evaporation chambers.
 7. A heatexchanger according to claim 6, wherein said interacting plates form athird duct system in which a third medium can circulate under heatexchange with at least said first medium.
 8. A heat exchanger accordingto claim 7, wherein said chambers include one delimited zone defined,and the outlet of said chambers is connected, via a compressor, to apart of said first duct system forming a condenser chamber having asubstantially vertical channel piloting said first medium from saidchamber's lower parts up into another delimited defined zone, whereinsaid first medium can circulate in said two delimited zones under heatexchange with itself.
 9. A heat exchanger according to claim 8, furthercomprising: a first duct chamber including an inlet and outlet allowingsaid second medium to enter said first duct chamber through said inletto be piloted through said first duct chamber under heat exchange withsaid first medium, and to leave said first duct chamber through saidoutlet, a plurality of interconnected evaporation chambers including acommon inlet, a common outlet and one delimited zone, allowing saidfirst medium to enter through said inlet to be piloted through saidevaporation chambers under heat exchange with said second medium andfurther through said zone under heat exchange with itself, and to leavesaid evaporation chambers through an outlet, a compressor and acondenser chamber including an inlet and an outlet, said condenserchamber further having another delimited zone and a substantiallyvertical channel leading to said other delimited zone from saidcondenser chamber's lower parts and said compressor being connected tosaid outlet and said inlet, allowing said first medium to be pilotedfrom said outlet into said condenser chamber through said inlet via saidcompressor and further piloted through said condenser chamber under heatexchange with said third medium, and further piloted up through saidchannel into and through said other zone through which said first mediumis allowed to be piloted under heat exchange with itself and thereafterto leave said condenser chamber through said outlet, an expansion valveconnected to said outlet and inlet allowing said first medium to bepiloted from said condenser chamber into said evaporation chambersthrough said inlet via said expansion valve, and a second duct chamberhaving an inlet and an outlet allowing said third medium to enter intosaid second duct chamber through said inlet and to be piloted throughsaid duct chamber under heat exchange with said first medium andallowing said third medium to leave said duct chamber through saidoutlet.
 10. A heat exchanger according to claim 6, wherein said drainagemeans is arranged to introduce said first medium back into theevaporation chambers through an external expansion means feeding saidinlet with said first medium.
 11. A heat exchanger according to of claim6, wherein said drainage means is arranged to introduce said firstmedium in an additional inlet by an expansion driven injector.
 12. Aheat exchanger according to claim 6, wherein said drainage meanscomprises a pump.
 13. A heat pump system, comprising an evaporatoraccording to claim
 1. 14. An air condition system, comprising anevaporator according to claim 1.